With traffic signal units provided for example at a road intersection or the like, if an illumination condition of the signal lights is abnormal, then a traffic conflict can result. In particular, if the green lights (referred to hereunder as G lights) for permitting people and vehicles to proceed, are simultaneously illuminated for the respective directions of the intersecting roads, an extremely dangerous situation results. To avoid this situation, monitoring for simultaneous illumination of the G lights for the respective directions of the intersecting roads has heretofore mainly involved using a hard logic, for example to detect the terminal voltage of the signal lights via a voltage transformer or the like.
With conventional simultaneous G light illumination detection methods, voltage transformers are connected across the terminals of the G lights, so that a voltage is produced in the respective voltage transformers when the G lights illuminate, the arrangement being such that when a G light pair for the respective directions of the intersecting roads are illuminated simultaneously, G light simultaneous illumination (danger condition) is advised by the presence of a voltage (corresponding to a high energy condition). That is to say, the arrangement is such that a danger condition is advised by a high energy condition. In this case, if a fault occurs where the output to the monitoring circuit itself, which includes for example the voltage transformer, has a fault giving zero, then there is a problem in that if a simultaneous illumination of the G light pair for the respective intersecting roads occurs, this cannot be advised.
Moreover, in most cases it has not been possible to reach a stage where the illumination condition of a plurality of signal lights is monitored by only monitoring for simultaneous illumination of a G light pair for respective intersecting roads.
In view of the above situation, it is an object of the present invention to provide a monitoring apparatus for fail-safe monitoring for abnormal conditions such as, simultaneous illumination of traffic proceed permit signal lights, or signal light burn-out. Moreover, it is an object of the invention to provide a signal light control apparatus, which uses such a fail-safe monitoring apparatus.